Electrically heated catalyst device

ABSTRACT

An electrically heated catalyst device has a cylindrical outer skin part and a cell formation part. A pair of electrodes formed on the outer skin park faces relative to each other in a radial direction of the honeycomb structural body. An electrode terminal is formed on the corresponding electrode in an outer radial direction of the honeycomb structural body. A length edge line of each electrode is inclined to a virtual reference line at a predetermined angle. The virtual reference line is a virtual line defined on the outer circumferential surface of the outer skin part and is parallel to the axial direction of the honeycomb structural body. The electrode terminals are formed at a predetermined interval in the axial direction of the honeycomb structural body to make an angle of less than 180° when viewed from one end surface perpendicular to the axial direction of the honeycomb structural body.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese Patent Application No. 2012-022880 filed on Feb. 6, 2012, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electrically heated catalyst (EHC) devices for purifying exhaust gas emitted from an internal combustion engine mounted to various systems such as motor vehicles.

2. Description of the Related Art

In general, a catalyst device is mounted to an exhaust gas pipe of an exhaust gas purifying system mounted to a motor vehicle. Exhaust gas emitted from the internal combustion engine passes through the exhaust gas pipe in the exhaust gas purifying system and is purified by the catalyst device. The purified exhaust gas is then discharged to the outside of the internal combustion engine of the motor vehicle. Such a catalyst device uses a honeycomb structural body which supports therein catalyst such as platinum (Pt), palladium (Pd), rhodium (Rh), etc.

By the way, it is necessary to heat the catalyst supported in the catalyst device at approximately 400° C. in order to adequately activate the catalyst. In order to increase the temperature of the catalyst device to a necessary temperature to activate catalyst, a conventional technique provides an electrically heated catalyst (EHC) device having a honeycomb structural body equipped with a pair of electrodes. The pair of the electrodes is formed on the outer circumferential surface of the honeycomb structural body. When an electrical power is supplied to the electrodes, current flows in the honeycomb structural body, and heat energy is generated therein.

For example, such an EHC device has a honeycomb structural body, a pair of electrodes, and a pair of electrode terminals. The honeycomb structural body has a cell formation part and an outer skin part of a cylindrical shape. The cell formation part is covered with the outer skin part. The pair of the electrodes is formed on an outer circumferential surface of the outer skin part of the honeycomb structural body so that one electrode faces the other electrode relative to each other in a radial direction of the honeycomb structural body. Each electrode terminal projects on the corresponding electrode toward the outside of the honeycomb structural body. The electrode terminals are electrically connected with the corresponding electrodes, respectively.

The EHC device having the above conventional structure is accommodated in a housing case and mounted to the exhaust gas pipe of the exhaust gas purifying system. The exhaust gas pipe in which the EHC device is installed is mounted to the installation space formed under the floor of the motor vehicle. When an outside power source supplies electric power to the electrodes through the electrode terminals in the EHC device, the honeycomb structural body is heated to activate catalyst supported in the honeycomb structural body.

The pair of the electrodes is formed on the outer skin part of the honeycomb structural body so as to face relative to each other in a radial direction of the honeycomb structural body. The electrode terminals are formed on the electrodes and electrically connected with the corresponding electrodes so that the electrode terminals face relative to each other at an angle of 180°.

Because the electrode terminals formed on the electrodes project in a radial direction toward the outside of the honeycomb structural body, the EHC device has a large size when viewed in a radial direction of the honeycomb structural body. So, there is a strong demand to decrease the size of the EHC device in such a radial direction of the honeycomb structural body because it is better to install the EHC device in a small installation area formed on the floor of a motor vehicle.

If at least one of the electrode terminals, which projects toward the outside in a radial direction of the honeycomb structural body, is mounted to the floor of the motor vehicle so that the electrode terminal faces the road surface relative to each other, condensed water is easily attached on the surface of the electrode terminal of the EHC device. As a result, there is a possibility of making a short circuit between the electrode terminal and the housing case of the EHC device. In order to eliminate this drawback, it is necessary to install the EHC device to the small installation part, for example, an exhaust gas pipe formed on floor of the motor vehicle so that the pair of the electrode terminals is parallel to the road surface, namely to the floor of the motor vehicle. However, this arrangement increases the size of the EHC device in the horizontal space.

For example, a conventional technique, disclosed in Japanese patent laid open publication No. JP H09-082457, has proposed an electrode structure used in an electrically heated catalyst device. In the electrode structure, electrodes of a bent shape and corresponding lead wires are arranged at a predetermined angle relative to each other. This electrode structure makes it possible to decrease the installation space to install the EHC device on the floor of a motor vehicle.

However, the electrodes having a bent shape is requested to use and electrically connect a connection member with each of the electrodes formed on the outer skin part of the honeycomb structure body with a connection member made of metal. The connection member made of metal is required to have a high thermal resistance because the EHC device is used in a harsh environment at a high temperature. In view of this, it is difficult to use the electrodes having a bent shape of the electrode in the EHC device. Accordingly, there is a strong demand in the conventional technical field to provide the EHC device having an improved structure to be installed in small installation space.

SUMMARY

It is therefore desired to provide an electrically heated catalyst (EHC) device having an improved structure to be installed in a small installation space to an exhaust gas purifying system of an internal combustion engine, for example, an engine of a motor vehicle.

An exemplary embodiment provides an electrically heated catalyst (EHC) device having a honeycomb structural body, a pair of electrodes, and a pair of electrode terminals. The honeycomb structural body has a cell formation part and an outer skin part. The cell formation part is covered with the outer skin part. The outer skin part has a cylindrical shape. The pair of the electrodes is formed on the outer circumferential surface of the outer skin part so that one electrode faces the other electrode relative to each other in a radial direction of the honeycomb structural body. It is possible for the electrodes to have various shapes such as a rectangle shape and a parallelogram shape. When each electrode has a parallelogram shape, a longitudinal edge in a length direction of the electrode will be referred to as the “length edge line”, and a width edge in a width direction will be referred to as the “width edge line”. The electrode terminal projects from the corresponding electrode toward the outside in a radial direction of the honeycomb structural body. The electrode terminals are electrically connected with the corresponding electrodes, respectively. Length edge lines of each of the electrodes formed on the outer circumferential surface of the outer skin part of the honeycomb structural body approximately extend along an axial direction X of the honeycomb structural body. That is, the length edge lines of each of the electrodes are not parallel to the axial direction of the honeycomb structural body. The length edge lines are inclined to a virtual reference line at a predetermined angle. The virtual reference line is parallel to the axial direction of the honeycomb structural body. The virtual reference line is a virtual straight line which runs on the outer skin part of the honeycomb structural body parallel to and along an axial direction of the honeycomb structural body. The virtual reference line extends parallel to the axial direction X of the honeycomb structural body. A gap or interval between the electrodes formed on the outer circumferential surface of the outer skin part of the honeycomb structural body is constant in a circumferential direction of the honeycomb structural body. Each of the electrode terminals in the pair is formed at a center part of the corresponding electrode in a circumferential direction of the honeycomb structural body. That is, the pair of the electrode terminals makes an angle of less than 180 degrees (180°) at a radial center of the honeycomb structural body when measured on the outer circumferential surface of the outer skin part and viewed down one end surface which is perpendicular to the axial direction of the honeycomb structural body of the EHC device.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a view showing an entire structure of an electrically heated catalyst (EHC) device according to a first exemplary embodiment of the present invention;

FIG. 2 is a view which explains the structure of the EHC device according to the first exemplary embodiment of the present invention when viewed from one end surface in an axial direction of the EHC device;

FIG. 3 is a view which explains the structure of the EHC device according to the first exemplary embodiment of the present invention when viewed from the other end surface in the axial direction of the EHC device;

FIG. 4 is a development view of an outer surface of the EHC device according to the first exemplary embodiment of the present invention;

FIG. 5 is a view showing a cross section of the EHC device installed in a housing case according to the first exemplary embodiment of the present invention;

FIG. 6 is a view which explains an installation structure of the EHC device according to the first exemplary embodiment of the present invention installed in an installation space in a motor vehicle when viewed from one end surface in an axial direction of the EHC device;

FIG. 7 is a view which explains the EHC device according to a second exemplary embodiment of the present invention when viewed from one end surface which is perpendicular to the axial direction X of the honeycomb structural body in the EHC device;

FIG. 8 is a view which explains the structure of the EHC device according to the second exemplary embodiment of the present invention when viewed from another end surface which is perpendicular to the axial direction X of the honeycomb structural body in the EHC device;

FIG. 9 is a development view of an external form of the EHC device according to the second exemplary embodiment of the present invention;

FIG. 10 is a view which explains an EHC device having a structure in which an insulation layer has the same thickness of an electrode layer according to the third exemplary embodiment of the present invention when viewed from one end surface in the axial direction X of the EHC device;

FIG. 11 is a view which explains the EHC device according to the third exemplary embodiment of the present invention when viewed from another end surface of the EHC device in the axial direction thereof;

FIG. 12 is a view showing a cross section of the EHC device installed in a housing case according to the third exemplary embodiment of the present invention;

FIG. 13 is a view which explains the EHC device having a structure in which an outer circumferential surface of the outer skin part and the electrodes formed on the outer skin part are covered with an insulation layer according to the third exemplary embodiment;

FIG. 14 is a view which explains the EHC device 5 having a different electrode structure according to a modification of the third exemplary embodiment of the present invention;

FIG. 15 is a view which explains the EHC device 5 having a different electrode structure according to a modification of the third exemplary embodiment of the present invention;

FIG. 16 is a view showing an entire structure of an EHC device as a comparison example;

FIG. 17 is a view showing an EHC device as a comparison example having electrodes and the electrode terminals formed on an outer circumferential surface so that one electrode faces the other electrode relative in opposite to each other in a radial direction of the honeycomb structural body 91 when viewed from the one end surface which is perpendicular to an axial direction of the EHC device 9; and

FIG. 18 is a view showing the EHC device as the comparison example when viewed from the other end surface which is perpendicular to an axial direction of the EHC device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.

An electrically heated catalyst (EHC) device according to a preferred exemplary embodiment of the present invention has a honeycomb structural body, a pair of electrodes, and a pair of electrode terminals. The honeycomb structural body has a cell formation part and an outer skin part. The cell formation part is covered with the outer skin part. The outer skin part has a cylindrical shape. The pair of the electrodes is formed on the outer skin part so that one electrode faces the other electrode relative to each other in a radial direction of the honeycomb structural body.

It is possible for the electrodes to have various shapes such as a parallelogram shape and a rectangle shape. When each electrode has a parallelogram shape, a longitudinal edge (or length edge) in a length direction of the electrode will be referred to as the “length edge line”, and a width edge in a width direction will be referred to as the “width edge line” as shown in FIG. 4.

The electrode terminals project from the corresponding electrodes toward an outer radial direction of the honeycomb structural body. The electrode terminals are electrically connected with the electrodes, respectively.

The cell formation part of the honeycomb structural body is composed of a plurality of porous partition walls arranged in a lattice shape and a plurality of cells. Each cell is surrounded by the porous partition walls. The cells extend along an axial direction of the honeycomb structural body.

It is preferable that the honeycomb structural body is made of porous ceramics containing SiC as the principal ingredient thereof. This makes it possible to provide the honeycomb structural body having an electrical conductivity and an expanded surface area.

The electrical conductivity of the honeycomb structural body can be changed by adjusting the chemical component of raw materials. Specifically, when the honeycomb structural body is made by SiC and impurities N, B, Al, etc. are dissolved in SiC in order to make a solid solution, it is possible to adjust the electrical conductivity of the honeycomb structural body by adjusting the quantity of N, B, Al, etc. in the solid solution of SiC.

When the honeycomb structural body is made of Si—SiC (Si—SiC is produced by impregnating SIC with Si), it is possible to adjust the electrical conductivity of the honeycomb structural body by adjusting a quantity of Si.

The porous partition walls in the cell formation part support catalyst. Such catalyst is capable of adsorbing harmful material such as carbon oxides, nitrogen oxides, hydrocarbons, etc. contained in exhaust gas emitted from an internal combustion engine. That is, the catalyst is capable of purifying the exhaust gas. In general, the honeycomb structural body in the EHC device uses a three-way catalyst which contains noble metals such as Pt, Pd, Rh, etc.

Next, in the structure of the EHC device according to the exemplary embodiment, the gap or interval between the electrodes in the pair is constant when measured on the outer circumferential surface of the outer skin part in a circumferential direction of the honeycomb structural body. When a virtual reference line (which will be explained in detail later) is defined, which runs on the outer circumferential surface of the outer skin part parallel to an axial direction of the honeycomb structural body, each of the length edge lines of each of the electrodes in the pair are not parallel to the virtual reference line, and runs on the outer circumferential surface of the outer skin part at a predetermined angle to the virtual reference line.

For example, when the pair of the electrodes is formed on the outer circumferential surface of the outer skin part of the honeycomb structural body so that the length edge lines of the electrodes are parallel to the virtual reference line, like the electrodes formed in a honeycomb structural body having a conventional structure, the electrodes in the pair are formed parallel to an axial direction of the honeycomb structural body. This increases the diameter direction of the EHC device and requires a large installation area in the inside of an exhaust gas pipe of an exhaust gas purifying system for an internal combustion engine.

Still further, when the length edge lines of the electrodes are parallel to the virtual reference line, the length edge lines of the electrodes are parallel to the axial direction of the honeycomb structural body. When electric power is supplied to the pair of the electrode terminals, the supplied electric power is concentrated at the length edge lines of the electrodes which are parallel to the virtual reference line. As a result, the thermal stress is concentrated along a specific axial direction of the honeycomb structural body. In this case, there is a possibility that the honeycomb structural body is damaged and broken because the generated thermal stress is forced into specified cells formed to extend along the EHC device.

On the other hand, in the structure of the EHC device according to the exemplary embodiment, the gap or interval between the electrodes in the pair measured along the circumferential direction of the honeycomb structural body is constant.

If the electrodes of the pair are slanted to one side on the outer circumferential surface of the outer skin part, one length edge line of one electrode becomes close to one length edge line of the other electrode, and the interval between these length edge lines of the electrodes in the pair is decreased. In this case, the interval between the other length edge line of one electrode and the other length edge line of the other electrode is expended. When electric power is supplied to the electrode terminals, the supplied electric power is concentrated at the length edge lines of the electrodes because the length between them is shortened. As a result, thermal stress is generated and concentrated at the length edge lines of the electrodes, and there is a possibility that the honeycomb structural body is damaged and broken.

Furthermore, if the length between the electrodes in the pair measured along the circumferential direction of the honeycomb structural body is not constant, there is a possibility that a current flows more easily in the part of the electrodes having the minimum interval between the electrodes. In this case, it is impossible to adequately and uniformly heat the entire of the honeycomb structural body when electric power is supplied to the electrode terminals.

In the structure of the EHC device according to the exemplary embodiment, it is preferable that a distance or interval, on the outer circumferential surface of the outer skin part, between the electrodes in the pair measured along the axial direction of the honeycomb structural body is larger than a distance or interval on the outer skin part between the electrodes along the circumferential direction of the honeycomb structural body.

In a structure in which the distance or interval between the electrodes measured along the axial direction is smaller than the distance between the electrodes measured along the circumferential direction, when electric power is supplied to the electrode terminals, there is a possibility that a current flows easily in the axial direction rather than in the circumferential direction on the outer circumferential surface of the outer skin part of the honeycomb structural body. As a result, this structure prevents the inside of the honeycomb structural body from being adequately and efficiently heated.

It is possible that the minimum distance between the electrodes in the pair measured in a radial direction of the honeycomb structural body is shorter than the minimum distance between the electrodes measured on the outer circumferential surface of the outer skin part. In this structure, when electric power is supplied to the electrode terminals, it is possible to prevent a current from flowing on the outer circumferential surface of the outer skin part of the honeycomb structural body. The minimum interval between the electrodes in the pair on the outer circumferential surface of the outer skin part is the distance between the length edge lines of the electrodes measured in the radial direction of the honeycomb structural body, where these length edge lines are close relative to each other along the circumferential direction of the honeycomb structural body.

It is possible to control the following intervals (or distances) by adjusting the width of each electrode in the circumferential direction C, the length of each electrode in the axial direction X, the diameter of the honeycomb structural body, the axial length of the honeycomb structural body, the angle of each length edge line of the electrodes to the virtual reference line 19 (or to the axial direction X shown in FIG. 4), etc.;

-   -   The interval between the electrodes in the pair measured on the         outer circumferential surface of the outer skin part along the         axial direction X;     -   The interval between the electrodes in the pair measured on the         outer circumferential surface of the outer skin part along the         circumferential direction C;     -   The minimum interval between the electrodes measured in the pair         in the radial direction Y of the honeycomb structural body; and     -   The minimum interval between the electrodes in the pair on the         outer circumferential surface of the outer skin part of the         honeycomb structural body.

It is preferable that each of the length edge lines of the electrodes is slanted to the virtual reference line 19 at an angle of not more than 45°.

This structure makes it possible to expand the distance between the electrodes in the pair measured on the outer circumferential surface of the outer skin part of the honeycomb structural body. It is therefore possible to prevent a current from flowing on the outer circumferential surface of the outer skin part when electric power is supplied to the electrode terminals. This makes it possible to uniformly and adequately heat the inside of the honeycomb structural body.

In the EHC device according to the exemplary embodiment, the entire of each of the length edge lines of the electrodes is slanted to the virtual reference line 19 (shown in FIG. 4, for example) at a predetermined angle. That is, each of the length edge lines of the electrodes is approximately formed parallel to the pair of the electrodes.

Further, it is possible to form the pair of the electrodes in a screw shape around the honeycomb structural body. This screw shape of each electrode indicates that each electrode is not formed around the whole circumferential surface of the outer skin part of the honeycomb structural body. The screw shape of each electrode indicates that each electrode is formed in less than (for example, ⅔ times) of the whole circumferential surface of the outer skin part of the honeycomb structural body.

It is preferable to form each of the electrodes with a uniform width along the circumferential direction of the honeycomb structural body. This structure makes it possible to easily form the electrodes on the outer circumferential surface of the outer skin part of the honeycomb structural body and to arrange the electrodes facing relative to each other in the honeycomb structural body. Further, it is possible for the electrodes of the pair to easily have the same distance or the same interval between them in the circumferential direction of the honeycomb structural body.

It is preferable that the honeycomb structural body has a relationship of D+E×sin θ1≧R/2, where reference character D designates a width of each of the electrodes measured along the circumferential direction C of the outer skin part of the honeycomb structural body, reference character E indicates a longitudinal length of each of the length edge lines of each of the electrodes, reference character θ1 denotes an angle of the length edge line of each of the electrodes to the virtual reference line. Reference character R indicates a circumference of an outer circumference of the honeycomb structural body in the circumferential direction C.

When electric power is supplied to the pair of the electrodes through the electrode terminals, this structure makes it possible to quickly increase a temperature of the cell formation part in the inside of the honeycomb structural body, through which exhaust gas passes. That is, this structure makes it possible to quickly activate catalyst such as a three-way catalyst supported in the cells inside of the honeycomb structural body. This can enhance the function of purifying exhaust gas emitted from an internal combustion engine.

If the relationship is not satisfied (for example, D+E×sin θ1<R/2), some catalyst supported in the cell formation part formed along the axial direction is not activated when electric power is supplied to the electrodes through the electrode terminals. This prevents exhaust gas from being completely purified because of generating non-activated catalyst in the honeycomb structural body, and because non-purified exhaust gas passes through the EHC device.

When the pair of the electrodes is formed on the outer circumferential surface of the outer skin part of the honeycomb structural body, it is possible to use one of conductive ceramics, metal, and metal alloy. There are SiC and Si—SiC as the conductive ceramics. Si—SiC is made by impregnating SiC with Si. There are metals such as Cr, Fe, Ni, Mo, Mn, Si, Ti, Nb, Al and alloys thereof to form the electrodes. It is preferable to use the conductive ceramics to form the electrodes.

Instead of using Si—SiC, it is also possible to use as conductive ceramics other conductive ceramics obtained by impregnating SiC with one or more selected from Si, Cr, Fe, Ni, and Al.

There are various methods of producing electrodes on the outer circumferential surface of the outer skin part of the honeycomb structural body. For example, there is a method of firing electrode material and of staking the obtained electrodes on the outer circumferential surface of the outer skin part of the honeycomb structural body by using adhesive. Further, there is another method of applying electrode paste on the outer circumferential surface of the outer skin part of the honeycomb structural body, and firing it. It is also possible to combine those methods.

The former method of staking the electrode on the outer circumferential surface of the outer skin part of the honeycomb structural body after firing the electrode will be explained in the first exemplary embodiment section.

In the latter method, at first electrode raw material is prepared. The electrode raw material is composed of SiC and one or more metal selected from Si, Cr, Fe, Ni, Al, etc. Binder, surfactant, pore forming agent, and water are added to the electrode raw material to make an electrode raw mixture. The electrode raw mixture is mixed to make electrode paste. A rubber on which an electrode formation area is formed is arranged on the outer circumferential surface of the outer skin part of the honeycomb structural body. The electrode paste produced by the above method is applied on the electrode formation area on the rubber arranged on the outer circumferential surface of the outer skin part. An extra electrode paste is removed by using a squeegee in order to from the flat surface on the electrode formation area. Next, the rubber is removed from the outer circumferential surface of the outer skin part of the honeycomb structural body so that the electrode paste is remained on the outer circumferential surface of the outer skin part of the honeycomb structural body. The honeycomb structural body with the electrode paste is fired at a predetermined temperature in order to make the electrodes on the honeycomb structural body.

It is preferable that an insulation layer made of electrical insulation material is formed on the outer skin part of the honeycomb structural body other than the electrode formation area on which the electrodes are formed.

The presence of the insulation layer makes it possible to enhance the insulation properties in the circumferential direction of the honeycomb structural body.

It is possible to form the insulation layer and the electrodes with the same thickness on the outer circumferential surface of the outer skin part of the honeycomb structural body. This makes it possible to make a flat surface of the outer circumferential surface of the honeycomb structural body without any step on the honeycomb structural body.

When the EHC device is accommodated in the housing case, a cushioning mat (or a resilient mat) having a predetermined elasticity is sandwiched between the outer circumferential surface of the EHC device and the housing case in order to supply a uniform pressure to the outer circumferential surface of the EHC device. This structure using the cushioning mat makes it possible to decrease the external stress applied to the EHC device.

It is also possible to form the insulation layer on the electrodes in addition to the area on the outer circumferential surface where no electrode is formed on the outer circumferential surface of the outer skin part of the honeycomb structural body. This can make the flat surface of the outer circumferential part of the honeycomb structural body without any step.

The insulation layer has a single layer structure made of electric insulation material. In addition to this, it is possible for the insulation layer to have a lamination structure having a plurality of insulation layers. When the insulation layer has such a lamination structure, it is possible to form each layer of the lamination structure with the same electric insulation material or a different electric insulation material.

It is preferable to form the insulation layer from electrically insulating material having the same mechanical properties as the electrodes. This makes it possible to reduce the thermal stress applied to the electrode and the entire of the honeycomb structural body. For example, it is possible to form the insulation layer with electric insulation material such as alumina, silicon oxide.

The EHC device according to the exemplary embodiment has a pair of the electrode terminals which is formed on the pair of the electrodes and projects toward the outer radial direction of the honeycomb structural body. It is possible to form the electrode terminals to extend from the corresponding electrode toward a direction which is perpendicular to a tangent of the outer circumference of the honeycomb structural body.

The electrode terminal has a pole shape and is made of conductive ceramics or conductive metal. It is preferable to form the electrode terminal with the conductive ceramics.

Each of the electrode terminals is formed on the center part of the corresponding electrode in the circumferential direction C on the outer circumferential surface of the outer skin part of the honeycomb structural body. When the electrode terminal is formed on a part which is apart from the center part of the electrode, there is a possibility of it being difficult to uniformly heat the entire of the honeycomb structural body when electric power is supplied to the electrode terminals.

When viewed from one end surface of the honeycomb structural body which is perpendicular to the axial direction X of the honeycomb structural body, the pair of the electrode terminals is formed to make an angle of less than 180° relative to each other. When the pair of the electrode terminals makes just the angle of 180°, that is, when the electrode terminals of the pair are formed parallel to each other, the radial dimension of the EHC device is increased in a radial direction. This structure of the electrode terminals needs having a large installation space in a motor vehicle.

Further, each of the electrode terminals of the pair is formed on the corresponding electrode so as to keep a predetermined interval or distance in the axial direction X of the honeycomb structural body. Because the pair of the electrodes is inclined at a predetermined angle to the virtual reference line on the outer circumferential surface of the outer skin part of the honeycomb structural body, it is possible to adjust the angle made by the electrode terminals of the pair when viewed from one end surface which is perpendicular to the axial direction X of the honeycomb structural body.

Reducing the angle between the electrode terminals of the pair makes it possible to reduce the installation space in the motor vehicle. So, it is preferable that the electrode terminals of the pair are separated by an angle of 150 degrees (150°), namely, make an angle of not more than 150 degrees (150°) when viewed along the axial direction, as shown in FIG. 2, FIG. 3, FIG. 7, FIG. 8, FIG. 10, FIG. 11, etc. It is more preferable to make an angle of not more than 120°, and most preferable to make an angle of not more than 90°.

First Exemplary Embodiment

A description will be given of the electrically heated catalyst device (EHC) 1 according to a first exemplary embodiment of the present invention with reference to FIG. 1 to FIG. 6.

FIG. 1 is a view showing an entire structure of the EHC device 1 according to the first exemplary embodiment. FIG. 2 is a view which explains the structure of the EHC device 1 according to the first exemplary embodiment when viewed from one end surface in an axial direction of the EHC device 1. FIG. 3 is a view which explains the structure of the EHC device 1 according to the first exemplary embodiment when viewed from the other end surface in the axial direction of the EHC device. FIG. 4 is a development view of an outer surface of the EHC device 1 according to the first exemplary embodiment.

As shown in FIG. 1 to FIG. 4, the EHC device 1 according to the first exemplary embodiment has the cell formation part 21, the honeycomb structural body 2, the pair of the electrodes 31 and 32, and the pair of the electrode terminals 310 and 320.

The honeycomb structural body 2 has the cell formation part 21 and the cylindrical outer skin part 22. The cell formation part 21 is covered with the cylindrical outer skin part 22. The pair of the electrodes 31 and 32 is formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 so that the electrodes 31 and 32 face relative to each other in a radial direction of the honeycomb structural body 2.

As previously described, it is possible for the electrodes to have various shapes such as a parallelogram shape and a rectangle shape. When each of the electrodes 31 and 32 has a parallelogram shape, as shown in FIG. 4, a longitudinal edge (or length edge) in a length direction of each electrode will be referred to as the “length edge line”, and a width edge in a width direction of each electrode will be referred to as the “width edge line”.

The electrode terminals 310 and 320 are formed on the electrodes 31 and 32, respectively, so as to project toward an outer radial direction of the EHC device 1.

As shown in FIG. 1 and FIG. 4, a virtual reference line 19 is defined, which is designated by a dotted line. The virtual reference line 19 present on the cylindrical outer skin part 22 is parallel to an axial direction X of the honeycomb structural body 2.

In particular, a length edge line 315 and a length edge line 325 as the part of the outline edge of the electrodes 31 and 32 extend approximately toward the axial direction X of the honeycomb structural body 2. Each of the length edge line 315 and the length edge line 325 is inclined at a predetermined angle θ1 to the virtual reference line 19.

As shown in FIG. 4, the EHC device 1 has the structure in which a gap A1 and B1 (B1=B1 a+B1 b) between the electrodes 31 and 32 has a constant value in a circumferential direction C of the honeycomb structural body 2. That is, the length B1 is the sum of B1 a and B1 b.

The electrode terminals 310 and 320 are formed at a center part of the electrodes 31 and 32, respectively, on the outer circumferential surface 221 of the outer skin part 22 of the honeycomb structural body 2 at a constant interval in the axial direction X.

As shown in FIG. 2 and FIG. 3, when the EHC device 1 is observed from one of the end surfaces 28 and 29 of the honeycomb structural body 2, the angle α between the electrode terminals 310 and 320 in the pair becomes less than 180°.

FIG. 2 shows the end surface 28 of the EHC device 1 when the EHC device 1 is observed from the side of the end surface 28. The electrode terminal 310 in the pair is shown at the near side and the electrode terminal 320 in the electrode terminal pair is shown at the back side.

On the other hand, FIG. 3 shows the end surface 29 of the EHC device 1 when the EHC device 1 is observed from the side of the end surface 29. The electrode terminal 310 in the electrode terminal pair is shown at the back side, and the electrode terminal 320 in the electrode terminal pair is shown at the near side.

Although FIG. 2, FIG. 3 and FIG. 4 do not show any cross section of each of the electrodes 31 and 32 formed on the outer circumferential surface 221 of the honeycomb structural body 2, the electrodes 31 and 32 are shown by hatching in order to show the positional relation between the electrodes. FIG. 7 to FIG. 11, FIG. 13 to FIG. 15, FIG. 17 and FIG. 18 show the electrodes by hatching in order to show the positional relation between the electrodes.

A description will now be given of the detailed structure of the EHC device 1 according to the first exemplary embodiment.

As shown in FIG. 1, FIG. 2 and FIG. 3, the honeycomb structural body 2 has the cell formation part 21 and the cylindrical outer skin part 22 which covers the cell formation part 21. The honeycomb structural body 2 has a cylindrical shape and has a diameter of 93 mm, and a length in the axial direction X of 100 mm. The honeycomb structural body 2 is made of porous ceramics composed of SiC as the principal ingredient thereof.

The cell formation part 21 has the porous partition walls 211 arranged in a lattice shape and a plurality of the cells 212. Each of the cells 212 is surrounded by the porous partition walls 211, and extends toward the axial direction X.

As shown in FIG. 1, FIG. 2 and FIG. 3, the pair of the electrodes 31 and 32 is formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. The electrodes 31 and 32 are made of conductive ceramics of Si—SiC composite material. The electrodes 31 and 32 face relative to each other on the outer circumferential surface 221 in a radial direction Y of the honeycomb structural body 2. As shown in FIG. 4, the electrodes 31 and 32 are formed on the outer circumferential surface 221 of the outer skin part 22 from one end surface 28 to the other surface 29 of the honeycomb structural body 2. As shown in FIG. 1, FIG. 2 and FIG. 3, one end surface 28 and the other surface 29 are perpendicular to the axial direction X of the honeycomb structural body 2.

As shown in FIG. 1 to FIG. 4, the length edge line 315 of the electrode 31 and the length edge line 325 of the electrode 32, which extend approximately toward the axial direction X of the honeycomb structural body 2, are formed, not in parallel with, but intersect with the virtual reference line 19. The virtual reference line 19 is a virtual line on the cylindrical outer skin part 22 along the axial direction X of the honeycomb structural body 2.

In the structure of the EHC device 1 according to the first exemplary embodiment, the electrodes 31 and 32 are formed along the axial direction X on the outer circumferential surface 221 of the cylindrical outer skin part 22 from the end surface 28 to the other end surface 29 of the honeycomb structural body 2. As shown in FIG. 4, when the length of the honeycomb structural body 2 along the longitudinal direction is C1, and the length of each of the length edge line 315 and the length edge line 316 is E1, the relationship of E1>C1 is satisfied. In the EHC device 1 according to the first exemplary embodiment, E1 is 138 mm, and C1 is 100 mm. As previously described, each of the length edge line 315 and the length edge line 316 is inclined to the virtual reference line 19 at the predetermined angle θ1 (θ1=42°). As shown in FIG. 1, the pair of the electrodes 31 and 32 is formed approximately in a screwed shape around the honeycomb structural body 2, namely, in a screw shape on the outer circumferential surface 221 of the cylindrical outer skin part 22.

As shown in FIG. 4, in the structure of the EHC device 1 according to the first exemplary embodiment, each of the length edge line 315 and the length edge line 316 is inclined at the predetermined angle θ1 (an acute angle) to the virtual reference line 19. That is, each of the length edge line 315 and the length edge line 316 and the virtual reference line 19 make the predetermined angle θ1. When each of the electrodes 31 and 32 has a wide D1 along the circumferential direction C, the longitudinal length of each of the length edge line 315 and the length edge line 316 is E1, and the length of the honeycomb structural body 2 along the circumferential direction C is R1, the following relationship is satisfied:

D1+E1×sin θ1≧R1/2.

In the structure of the honeycomb structural body 2 of the EHC device 1 according to the first exemplary embodiment, D1 is 60 mm, E1 is 138 mm, θ1 is 42°, and R1 is 292 mm.

As shown in FIG. 4, the edge point Ea of the electrode 31 and the edge point Eb of the electrode 32 intersects in the axial direction X with the virtual reference line 19 defined on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2 in the EHC device 1 according to the first exemplary embodiment. More specifically, each of the electrodes 31 and 32 intersects at the edge point E1, Eb with the same virtual reference line 19. Further, the distance F1 between the electrodes 31 and 32 in the axial direction X on the outer circumferential surface 221 is larger than the gap A1, B1 between the electrodes 31 and 32 on the outer circumferential surface 221 in the circumferential direction C.

In the structure of the honeycomb structural body 2 of the EHC device 1 according to the first exemplary embodiment, D1 is 60 mm, F1 is 100 mm, A1 is 88 mm, B1 a is 26 mm, B1 b is 26 mm, B1=B1 a+B1 b=88 mm, and A1=B1.

As shown in FIG. 1, FIG. 2 and FIG. 3, the electrode terminals 310 and 320 are formed on the electrodes 31 and 32, respectively. Each of the electrode terminals 310 and 320 is made of conductive ceramics such as Si—SiC composite material. Each of the electrode terminals 310 and 320 has a cylindrical shape. The electrode terminals 310 and 320 are projected from the electrodes 31 and 32 on outer circumferential surface 221 toward an outer radial direction of the honeycomb structural body 2.

As shown in FIG. 4, each of the electrode terminals 310 and 320 is formed at a center part of the corresponding electrode in the circumferential direction C of the honeycomb structural body 2. That is, when the width of each of the electrodes 31 and 32 in the circumferential direction C is D1, each of the electrode terminals 310 and 320 is formed at the half (D 1/2) of the width D1 of the corresponding electrode.

Further, as shown in FIG. 1 and FIG. 4, the electrode terminals 310 and 320 are formed on the corresponding electrodes 31 and 32, respectively so that the electrode terminals 310 and 320 keep a predetermined interval.

In the structure of the EHC device 1 according to the first exemplary embodiment, the electrode terminal 310 is formed closer to one end surface 28 of the honeycomb structural body 2 than the other end surface 29 along the axial direction X of the honeycomb structural body 2. On the other hand, the electrode terminal 320 is formed closer to the other end surface 29 of the honeycomb structural body 2 than the end surface 28 along the axial direction X of the honeycomb structural body 2.

Still further, as shown in FIG. 2, the pair of the electrode terminals 310 and 320 makes an angle α1 of 80° (α1=80°) when the EHC device 1 is observed from one end surface 28. Similarly, as shown in FIG. 3, the pair of the electrode terminals 310 and 320 makes the angle α1 of 80° (α1=80°) when the EHC device 1 is observed from one end surface 29.

As previously described, the pair of the electrode terminals 310 and 320 is formed on the electrodes 31 and 32 to keep the predetermined interval in the axial direction X of the honeycomb structural body 2 in order to make the angle α1 of 80° (α1=80°).

As shown in FIG. 1, electric power is supplied form an outside power source (not shown) to the electrode terminals 310 and 320 of the electrodes 31 and 32 in the EHC device 1. Catalyst is supported on the surfaces of the cells surrounded by the porous partition walls 211 in the cell formation part 21 of the honeycomb structural body 2. The first exemplary embodiment uses a three-way catalyst as noble metals such as Pt, Pd, Rh, etc.

When the outside power source (not shown) supplies electric power to the pair of the electrodes 31 and 32, the honeycomb structural body 2 is heated and the catalyst supported on the surface of the porous partition walls 211 is activated.

Next, a description will now be given of a method of manufacturing the EHC device 1 according to the first exemplary embodiment with reference to FIG. 1, FIG. 2 and FIG. 3.

First, the honeycomb structural body 2 is produced by using a known manufacturing method, which is made of porous ceramics such as SiC, and a three-way catalyst is supported on the surfaces of the porous partition walls in the honeycomb structural body 2.

Next, the pair of the electrodes 31 and 32 is formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2.

Specifically, a sheet-shaped electrode material is cut and molded with a predetermined size. The sheet-shaped electrode material 221 having the predetermine size is fired in order to make the electrodes 31 and 32 made of composite material Si—SiC.

Next, the electrodes 31 and 32 made of Si—SiC composite material are adhered on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2 by using adhesive paste which contains Si—SiC composite material, carbon, binder, etc., as shown in FIG. 1.

The honeycomb structural body 2 with the electrodes 31 and 32 formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 is fired at a predetermined temperature (approximately 1600° C. under a predetermined gas (Ar, at ordinary pressure). This makes the pair of the electrodes 31 and 32 fixed onto the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2.

Next, electrode terminal material containing conductive ceramics is molded in a cylindrical shape and is fired in order to make the electrode terminals 310 and 320. That is, the electrode terminals 310 and 320 are made of Si—SiC composite material (conductive material).

Next, the electrode terminals 310 and 320 are fixed on the electrodes 31 and 32 formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 by using adhesive paste which contains Si—SiC composite material, carbon, binder, etc.

As shown in FIG. 1, this completes the production of the EHC device 1 having the pair of the electrodes 31 and 32 and the pair of the electrode terminals 310 and 320. The pair of the electrodes 31 and 32 is formed in a radial direction on the outer circumferential surface 221 of the cell formation part 21 of the honeycomb structural body 2. The pair of the electrode terminals 310 and 320 is projected from the electrodes 31 and 32 toward the outside in a radial direction of the honeycomb structural body 2.

FIG. 5 is a view showing a cross section of the EHC device 1 stored in a housing case 10 made of metal according to the first exemplary embodiment of the present invention.

As shown in FIG. 5, the EHC device 1 is stored in the housing case 10. A cushioning mat 12 (or a resilient mat) made of fiber is placed between the metal housing case 10 and the EHC device 1. In the EHC device 1, the electrode terminal 310 made of conductive ceramics is electrically connected with a lead wire 312 through a metal terminal 311. Although the electrode terminal 320 is not shown in FIG. 5, the electrode terminal 320 made of conductive material is electrically connected with a lead wire 322 through a metal terminal 320 like the structure of the electrode terminal 310.

The electrode terminal 310 is electrically connected with the metal terminal 311. For example, the electrode terminal 310 is electrically connected with the metal terminal 311 by brazing. In addition, the metal terminal 311 has a stress relaxing structure (not shown) in order to absorb a misregistration generated between the housing case 10, and a misregistration generated between the housing case 10 and the electrode terminal 310.

The metal electrode 311 and the lead wire 312 are caulked together in order to fix them.

FIG. 6 is a view which explains an installation structure of the EHC device 1 according to the first exemplary embodiment of the present invention which is installed in an installation space under the floor of a motor vehicle when viewed from one end surface in an axial direction of the EHC device 1.

As shown in FIG. 6, the installation space under the floor of a motor vehicle having the EHC device 1 is limited because there are the frame and the body under the floor of the motor vehicle. As shown in FIG. 6, a gap M, a gap N and an angle β between the EHC device 1 and a heat shield plate 199 are 150 mm, 115 mm, and 20°, respectively (M=150 mm, N=115 mm, and β=20°).

Next, a description will now be given of the actions and effects of the EHC device 1 according to the first exemplary embodiment of the present invention.

As previously described and shown in FIG. 1, FIG. 2 and FIG. 3, the EHC device 1 according to the first exemplary embodiment has the structure in which the electrode terminals 310 and 320 in the pair make the angle α1 of 80° (α1=80°) and the electrode terminals 310 and 320 in the pair make an angle of less than 180°. This structure makes it possible to reduce the dimension Y in a radial direction of the honeycomb structural body 2. It is possible to reduce the installation space under the floor of a motor vehicle when the EHC device 1 is mounted to an exhaust gas pipe in the installation space in the motor vehicle. Further, as shown in FIG. 5 and FIG. 6, the structure of the EHC 1 makes it possible for a motor vehicle to have the installation space so that the pair of the electrode terminals 310 and 320 is positioned above the horizontal line HO which passes through the center of the honeycomb structure body 2 when the EHC device 1 is fixed to the exhaust gas pipe of the motor vehicle.

Further, as shown in FIG. 4, the EHC device 1 has the constant gap A1 and the constant gap B1 (B1=B1 a+B1 b) formed between the pair of the electrodes 31 and 32 in a circumferential direction C of the honeycomb structural body 2. In addition to this, each of the length edge lines 315 and 325 of the electrodes 31 and 32, which extend toward the axial direction X of the honeycomb structural body 2, is inclined to the virtual reference line 19 at the angle θ1 (θ1=42°). This makes it possible to have the pair of the electrode terminals 310 and 320 having the angle of less than 180° by forming the pair of the electrode terminals 310 and 320 at the center position of the electrodes 31 and 32 in the circumferential direction C of the honeycomb structural body 2 and arranging the electrode terminals 310 and 320 at a predetermined interval in the axial direction X of the honeycomb structural body 2. The first exemplary embodiment uses the angle θ1 of 42° (θ1=42°). However, the concept of the present invention is not limited by this structure. For example, it is possible to arrange the pair of the electrode terminals 310 and 320 at a different angle of less than 180° other than the angle θ1 of 42°.

Still further, as shown in FIG. 2 and FIG. 3, the honeycomb structural body 2 of the EHC device 1 is covered with the cylindrical outer skin part 22. That is, the honeycomb structural body 2 has a cross section of a circle shape when cut in a direction which is perpendicular to the longitudinal direction of the honeycomb structural body 2.

In the structure of the pair of the electrodes 31 and 32 formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2, a distance in a radial direction (or a radial distance) between the electrodes 31 and 32 has a different distance according to the position along the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. That is, the radial distance between the electrodes 31 and 32 has the minimum value when the position on the outer circumferential surface is at the circumferential edge part of the electrodes, which is far from the center position of the electrodes of the outer circumferential surface 221. On the other hand, the radial distance between the electrodes 31 and 32 has the maximum value when the position on the outer circumferential surface is at the circumferential center position of each of the electrodes 31 and 32 on the outer circumferential surface 221. The more a current easily flows when the opposed position is shifted from the center of the electrode to the edge of the electrode in the circumferential direction of the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. This makes it possible to concentrate electric power at the length edge lines 315 and 325 of the electrodes 31 and 32 because the opposed distance (A1 and B1 shown in FIG. 4) between the electrodes 31 and 32 has the minimum distance in a cross section of honeycomb structural body 2.

As shown in FIG. 1 and FIG. 4, when the virtual reference line 19 is defined on the outer circumferential surface of the outer skin part in the honeycomb structural body 2 in the EHC device 1 according to the first exemplary embodiment, the length edge lines 315 and 325, which extend approximately toward the axial direction of the honeycomb structural body 2, are arranged so as to intersect with the virtual reference line 19. That is, in the structure of the EHC device 1 according to the first exemplary embodiment, the length edge lines 315 and 325 are formed on the outer circumferential surface 221 of the cylindrical outer skin part 22 so that the length edge lines 315 and 325 are not parallel to the axial direction X of the honeycomb structural body 2, namely, not parallel to the virtual reference line 19.

Because the length edge lines 315 and 325 are not parallel to the axial direction X of the honeycomb structural body 2 even if supplied electric power is concentrated to the area of the length edge lines 315 and 325, it is possible to prevent thermal stress from being concentrated along the axial direction X of the honeycomb structural body 2. That is, it is possible to avoid the thermal stress from being concentrated at the specific one or some cells extending along the axial direction X, and to diffuse and relax the thermal stress into a plurality of the cells 212. This can avoid the honeycomb structural body 2 in the EHC device 1 from being damaged and broken by the thermal stress.

As shown in FIG. 1 to FIG. 4, the electrode terminals 310 and 320 in the pair are formed in a circumferential direction of the honeycomb structural body 2 on the center part of the electrodes 31 and 32 in the pair, respectively. This makes it possible to uniformly heat the entire of the honeycomb structural body 2 when electric power is supplied to the electrode terminals 310 and 320.

Further, in the structure of the EHC device 1 according to the first exemplary embodiment, the gap A1 and the gap B1 measured between the electrodes 31 and 32 in the pair along the circumferential direction C of the outer circumferential surface 221 of the cylindrical outer skin part 22 are the same distance (A1=B1), as shown in FIG. 4. That is, the gap A1 and the gap B1 between the length edge lines 315 and 325 of the electrodes 31 and 32 along the circumferential direction C are the same length. The electrodes 31 and 32 have the same length in the longitudinal direction thereof. That is, the electrode 31 does not approach the electrode 32 along the circumferential direction C so that one electrode 31 faces the other electrode 32 at the constant gaps A1 and B1 (A1=B1). It is possible to increase the area between the electrodes 31 and 32 on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. This makes it possible to uniformly heat the entire of the honeycomb structural body 2. Still further, this structure of the honeycomb structural body 2 makes it possible to have the same gaps A1 and B1 between the length edge lines 315 and 325 of the pair of the electrodes 31 and 32 (A1=B1, B1=B1 a+B1 b shown in FIG. 4). It is thereby possible to prevent the honeycomb structural body 2 from being damaged and broken by thermal stress because the gap between the length edge lines of the electrodes 31 and 32 is constant and this prevents electric power from being concentrated in the specific area between the length edge lines.

In the structure of the EHC device 1 according to the first exemplary embodiment, the honeycomb structural body 2 has the outer skin part 22 of a cylindrical shape and the entire of the honeycomb structural body 2 has approximately a cylinder shape. This allows workers to easily handle the EHC device 1. For example, it is possible to easily install the EHC device 1 to the inside of the exhaust gas pipe of the internal combustion engine mounted to a motor vehicle. Further, it is possible to install the ECH device 1 to the exhaust gas pipe while a uniform force is applied to the outside surface of the EHC device 1. This makes it possible to suppress the EHC device 1 from having cracks and being broken. It is accordingly for the worker to install the EHC device 1 easily in the exhaust gas pipe of the internal combustion engine of the motor vehicle.

Still further, because the honeycomb structural body 2 is made of porous ceramics composed of SiC, it is possible for the honeycomb structural body 2 to have a good conductivity, and for the honeycomb structural body 2 to have a large surface area.

Still further, as shown in FIG. 4, the electrodes 31 and 32 in the pair intersect with the same virtual reference line 19 on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. The interval F1 between the electrodes 31 and 32 in the pair in the axial direction X on the outer circumferential surface 221 of the honeycomb structural body 2 is larger than the gap A1 (=B1) between the length edge lines of the electrodes 31 and 32 along the circumferential direction C.

On the other hand, when the distance F1 is smaller than the gap A1 (or B1), there is a possibility of preventing a current flow in the axial direction X on the outer circumferential surface 221 of the cylindrical outer skin part 22 of the honeycomb structural body 2. This prevents the inside of the honeycomb structural body 2 from being adequately heated when electric power is supplied to the electrode terminals 310 and 320.

Furthermore, as shown in FIG. 4, in the structure of the EHC device 1 according to the first exemplary embodiment, the relationship of D1+E1×sin θ1≧R1/2, where reference character θ1 designates the angle (an acute angle) formed between the virtual reference line 19 and the length edge lines of each of the electrodes 31 and 32, reference character D1 denotes the width of each of the electrodes 31 and 32 in the circumferential direction C, reference character E1 indicates the length of each of the length edge lines 315 and 325 of the electrodes 31 and 32, and reference character R1 indicates the circumference of the outer circumference of the honeycomb structural body 2 along the circumferential direction C.

As shown in FIG. 1, FIG. 2 and FIG. 3, when electric power is supplied to the electrode terminals 310 and 320 in the honeycomb structural body 2 which supports a three-way catalyst, for example, it is possible to quickly activate the three-way catalyst supported by the cells formed in the part of the cell formation part 21, through which exhaust gas flows. This structure makes it possible to increase the exhaust-gas purifying capability of the EHC device 1.

Still further, as shown in FIG. 1, when a power source (omitted from FIG. 1) supplies electric power to the pair of the electrodes 31 and 32 through the pair of the electrode terminals 310 and 320 (omitted from FIG. 1), the honeycomb structural body 2 of the EHC device 1 according to the first exemplary embodiment is uniformly heated. This makes it possible to activate the catalyst such as a three-way catalyst supported in the inside of the honeycomb structural body 2, and to quickly start the function of purifying exhaust gas emitted from the internal combustion engine of the motor vehicle.

Second Exemplary Embodiment

A description will be given of an electrically heated catalyst (EHC) device 4 according to the secondary exemplary embodiment of the present invention with reference to FIG. 7, FIG. 8 and FIG. 9.

FIG. 7 is a view which explains the EHC device 4 according to the second exemplary embodiment when viewed from one end surface which is perpendicular to the axial direction X of a honeycomb structural body 40 in the EHC device 4. FIG. 8 is a view which explains the structure of the EHC device 4 according to the second exemplary embodiment when viewed from another end surface which is perpendicular to the axial direction X of the honeycomb structural body 40 in the EHC device 4. FIG. 9 is a development view of an external form of the EHC device 4 according to the second exemplary embodiment of the present invention.

As shown in FIG. 7, FIG. 8 and FIG. 9, similar to the structure of the EHC device 1 according to the first exemplary embodiment, the EHC device 4 according to the secondary exemplary embodiment has a honeycomb structural body 40, a pair of an electrode 45 and an electrode 46, and a pair of electrode terminals 45 and 46. The honeycomb structural body 40 has a cell formation part 41 and a cylindrical outer skin part 42. The electrode 45 and the electrode 46 are formed and arranged on the outer circumferential surface 421 of the outer skin part 42 of the honeycomb structural body 40 so that the electrode 45 faces the electrode 46 relative to each other in a circumferential direction C. The pair of the electrode terminals 450 and 460 projects toward the outside of a radial direction Y of the honeycomb structural body 40 on the pair of the electrode 45 and 46.

As shown in FIG. 9, one electrode terminal 450 in the pair of the electrode terminals 450 and 460 is formed on the electrode 45 formed on the outer circumferential surface 421 of the outer skin part 42 of the honeycomb structural body 40. Like the structure of the electrode terminal 310 in the honeycomb structural body 2 according to the first exemplary embodiment, the electrode terminal 450 is formed, on the electrode 45, close to one end surface 408 in the axial direction X of the honeycomb structural body 40.

On the other hand, the other electrode terminal 460 in the pair is formed on the electrode 46 formed on the outer circumferential surface 421 of the outer skin part 42 of the honeycomb structural body 40. That is, as shown in FIG. 9, the electrode terminal 460 is formed at the center part of the electrode 46 when viewed along the axial direction X of the honeycomb structural body 40 and at the center part of the width of the electrode 46 in the circumferential direction C. Other components of the EHC device 4 according to the secondary exemplary embodiment have the same of those of the EHC device 1 according to the first exemplary embodiment. That is, the length edge lines 455 and 465 of the electrodes 45 and 46 are not formed parallel to the virtual reference line 49 and are inclined to the virtual reference line 49 at a predetermined angle θ1 of 42° (θ1=42°). Accordingly, as shown in FIG. 7 and FIG. 8, when viewed from the one end surface 408 or the other end surface 409 along the axial direction X of the honeycomb structural body 40 in the EHC device 4 according to the second exemplary embodiment, the angle α2 which is made by the electrode terminals 450 and 460 is larger than the angle α1 used in the structure of the EHC device 1 according to the first exemplary embodiment. That is, the second exemplary embodiment uses the angle α2 of 150° (α2=150°).

As previously described, the relative position between the electrode 45 and the electrode 46 when viewed along the axial direction of the honeycomb structural body 40 is changed, which is different from the structure in the first exemplary embodiment, it is possible to easily change the angle made by the pair of the electrode terminals 450 and 460. Further, it is possible to optionally change the angle made by the pair of the electrode terminals by changing the diameter of the honeycomb structural body, the size in the longitudinal direction (axial direction X) of the honeycomb structural body, and the angle of the electrodes formed on the outer circumferential surface to the virtual reference line.

The EHC device 4 according to the second exemplary embodiment has the same structure of the EHC device 1 according to the first exemplary embodiment other than the angle of the electrode terminals 450 and 460. Therefore it is possible for the EHC device 4 according to the second exemplary embodiment to have the same actions and effects of the EHC device 1 according to the first exemplary embodiment.

Third Exemplary Embodiment

A description will be given of an electrically heated catalyst (EHC) device 5 according to the third exemplary embodiment of the present invention with reference to FIG. 10 to FIG. 15.

FIG. 10 is a view which explains the EHC device 5 having a structure in which an insulation layer has the same thickness of an electrode layer according to the third exemplary embodiment of the present invention when viewed from one end surface in an axial direction of the EHC device 5. FIG. 11 is a view which explains the EHC device 5 according to the third exemplary embodiment of the present invention when viewed from another end surface of the EHC device 5 in the axial direction thereof.

The third exemplary embodiment shows the EHC device 5 having a structure in which an insulation layer is formed on the area other than the electrodes on a cylindrical outer skin part 52.

As shown in FIG. 10 and FIG. 11, similar to the EHC device 1 according to the first exemplary embodiment, the EHC device 5 according to the third exemplary embodiment has a honeycomb structural body 50, a pair of an electrode 55 and an electrode 56, and a pair of electrode terminals 550 and 560. The honeycomb structural body 50 has a cell formation part 51 and the outer skin part 52 having a cylindrical shape. The electrode 55 and the electrode 56 are formed and arranged on the outer circumferential surface 521 of the outer skin part 52 of the honeycomb structural body 50 so that the electrode 55 faces the electrode 56 in the circumferential direction C. The pair of the electrode terminals 550 and 560 projects toward the outside of the radial direction Y of the honeycomb structural body 50 on the pair of the electrode 55 and 56.

Similar to the structure of the EHC device 1 according to the first exemplary embodiment, the pair of the electrode terminals 550 and 560 is formed so that the electrode terminals 550 and 560 make an angle α1 of 80° (α1=80°) when the EHC device 5 is observed from one of the end surfaces 508 and 509 (namely, in the axial direction X which is perpendicular to the end surface 508 shown in FIG. 10 and the end surface 509 shown in FIG. 11).

In particular, the insulation layer 53 is formed on the area other than the electrode formation area, on which the electrodes 55 and 56 are formed on the outer skin part 52 of the honeycomb structural body 50. The insulation layer 53 has the same thickness of each of the electrode 55 and the electrode 56 and is formed on the area other than the electrode formation area in the outer skin part 52. The insulation layer 53 is made of SiO₂. It is possible to use Al₂O₃ instead of to use SiO₂. The insulation layer 53 can be formed by applying insulation material such as SiO2 on the outer skin part 52 of the honeycomb structural body 50 and by firing it. It is also possible to form the insulation layer 53 by chemical reaction.

The EHC device 5 according to the third exemplary embodiment has the same structure of the EHC device 1 according to the first exemplary embodiment other than the presence of the insulation layer 53.

Because the EHC device 5 according to the third exemplary embodiment has the insulation layer 53 formed on the area other than the electrode formation area of the electrodes 55 and 56 on the outer skin part 52 of the honeycomb structural body 50, it is possible to increase the electric insulation capability in the circumferential direction C of the honeycomb structural body 50.

FIG. 12 is a view showing a cross section of the EHC device 5 installed in the housing case 10 according to the third exemplary embodiment of the present invention.

As shown in FIG. 12, the EHC device 5 according to the third exemplary embodiment is stored in the housing case 10 in which the cushioning mat 12 having elasticity, for example, made of fiber is placed between the metal housing case 10 and the EHC device 5. In the EHC device 5, because the insulation layer 53 is formed on the outer skin part 52 of the honeycomb structural body 50, it is possible to enhance the insulation properties between the honeycomb structural body 50 and the housing case 10 made of metal, and between the housing case 10 and the length edge lines 551 and 561 of the electrodes 55 and 56.

Further, because the insulation layer 53 has the same thickness of the electrodes 55 and 56 formed on the outer skin part 52 of the honeycomb structural body 50, it is possible to provide the flat surface of the outer circumferential surface 521 on the insulation layer 53 and the electrodes 55 and 56. This structure makes it possible to provide a uniform surface stress to be applied onto the outer periphery of the EHC device 5 when the EHC device 5 is accommodated in the housing case 10 and the cushioning mat 12 is stacked between the EHC device 5 and the housing case 10. This can enhance the stress reduction effect of the cushioning mat 12, and to prevent the honeycomb structural body 50 from being damaged and broken when the EHC device 5 is assembled with the housing case 10 (by a canning process). Still further, this structure makes it possible to prevent the honeycomb structural body 50 and the electrodes 55 and 56 from being cracked by thermal shock of exhaust gas.

In the EHC device 5, because the insulation layer 53 is made of SiO₂ and the electrodes 55 and 56 are made of material which is similar mechanical properties of SiO₂, this structure makes it possible to reduce the thermal stress of the honeycomb structural body 50. For example, this structure makes it possible to reduce Young modulus of the honeycomb structural body 50 as the mechanical properties. That is, it is preferable for the electrodes 55 and 56 and the insulation layer 53 to have the same Young modulus or a similar Young modulus. Still further, it is preferable for the honeycomb structural body 50 and the electrodes 55 and 56 and the insulation layer 53 to have the same coefficient of linear expansion or a similar coefficient of linear expansion.

Still further, the EHC device 5 according to the third exemplary embodiment has the same structure and the same actions and effects of the EHC device 1 according to the first exemplary embodiment other than the presence of the insulation layer 53.

In the structure of the EHC device 5 according to the third exemplary embodiment, the insulation layer 53 is formed on the area other than the electrode formation area on the outer skin part 52 of the honeycomb structural body 50. However, the concept of the present invention is not limited by this structure.

FIG. 13 is a view which explains the EHC device 5 having another structure in which the electrodes 55 and 56 are completely covered with an insulation layer 53-1. In other words, the outer skin part 52 is completely covered with the insulation layer 53-1. In this structure, the insulation layer 53-1 is the most outer layer of the honeycomb structural body 50. This structure of the honeycomb structural body 50 makes it possible to avoid the honeycomb structural body 50 from being damaged and cracked possible to increase assembling workability of the honeycomb structural body 50 into the housing case 10. Still further, this structure makes it possible to provide the increases insulation capability and to prevent current leakage and to prevent the electrodes 55 and 56 and the housing case 10 from making a short circuit.

The third exemplary embodiment shown in FIG. 10 and FIG. 11 and the modification thereof shown in FIG. 13 show the structure of the EHC device 5 in which the length edge lines 551 and 561 of the pair of the electrodes 55 and 56 are formed perpendicular to the outer circumferential surface 521 of the outer skin part 52 of the honeycomb structural body 50, and the insulation layer 53 and 53-1 is formed on the outer circumferential surface 521 of the outer skin part 52 of the honeycomb structural body 50.

However, the concept of the present invention is not limited by this. For example, it is possible for the EHC device to use a different structure of the electrodes.

FIG. 14 is a view which explains the EHC device 5 having a different electrode structure according to the modification of the third exemplary embodiment of the present invention.

As shown in FIG. 14, the EHC device 5 has a different electrode structure in which the length edge line 553 of the electrodes 55-1 has a step shape and the length edge line 563 of the electrode 56 has a step shape in the honeycomb structural body 5 when viewed from one end surface 51 of the honeycomb structural body 5, which is perpendicular to the axial direction X of the honeycomb structural body 5.

FIG. 15 is a view which explains the EHC device 5 having a different electrode structure according to the modification of the third exemplary embodiment of the present invention.

As shown in FIG. 15, the length edge line 554 of the electrodes 55-2 has a slope shape and the length edge line 564 of the electrode 56-2 has a slope shape in the honeycomb structural body 5 when viewed from one end surface 51 of the honeycomb structural body 5, which is perpendicular to the axial direction X of the honeycomb structural body 5.

The electrode structures shown in FIG. 14 and FIG. 15 make it possible to further promote the concentration of current at the length edge lines of the electrodes in the honeycomb structural body 5 when electric power is supplied to the electrode terminals 550 and 560.

That is, because the interval between the electrodes 55-1 and 56-1, 55-2 and 56-2 becomes shorter from the center part toward the edge of the electrodes in the circumferential direction C of the honeycomb structural body, a current flows easily in the edge rather than in the center part of the electrodes. That is, the gap between the length edge lines of the electrodes is shorter than the gap between the gap between the center parts of both the electrodes, where the electrodes are extended approximately along the axial direction X of the honeycomb structural body. Therefore a current flows easily at the length edge lines of the electrodes rather than the center part thereof and supplied electric power is more concentrated at the length edge lines of the electrodes.

On the other hand, when the electrodes have the step shape 553, 563 shown in FIG. 14 or the slope shape 554, 564 shown in FIG. 15, the thickness of each of the electrode is decreased at the length edge lines rather than the center part of the electrodes. This structure makes it possible to increase an electric resistance at the length edge lines of the electrodes. The structure of the electrodes shown in FIG. 14 and FIG. 15 prevents the current from being concentrated at the length edge lines of the electrodes. As a result, this makes it possible to more decrease the magnitude of the stress applied to the honeycomb structural body 50 in addition to the effect in which the electrodes are formed to incline to the axial direction X on the outer skin part of the honeycomb structural body.

In particular, the combination of the features (a) and (b) is more effective when the honeycomb structural body having a low strength is used in the EHC device:

(a) the electrodes are inclined at a predetermined angle to the axial direction X of the honeycomb structural body; and

(b) the edges of the electrodes have the step shape or the slope shape (see FIG. 14 and FIG. 15).

As previously described, even if the step part or the slope part is formed in the electrodes, it is possible for the honeycomb structural body to have a flat surface by forming the insulation layer between the electrodes on the outer skin part, as shown in FIG. 14 and FIG. 15. The presence of the insulation layer makes it possible to increase the electric insulation function along the circumferential direction C of the honeycomb structural body 50. Further, the presence of the insulation layer makes it possible to increase the electrical insulation between the housing case 10 and the honeycomb structural body 50, and the electrical insulation between the housing case 10 and the length edge lines of the electrodes when the honeycomb structural body 50 is accommodated in the housing case 10. This makes it possible to prevent the honeycomb structural body 50 from being damaged and broken when the honeycomb structural body 50 is assembled with the housing case 10. Still further, this makes it possible to prevent the honeycomb structural body 50 in the EHC device from being cracked and broken by thermal stress generated by exhaust gas when the EHC device is used in an exhaust gas purifying system of an internal combustion engine of a motor vehicle.

Still further, even if the step shapes 553 and 563 or the slope parts 554 and 564 are formed at the length edge lines of the electrodes, it is possible to have a structure in which the electrodes are completely covered with the insulation layer. This structure makes it possible to provide easy assembling of the honeycomb structural body with the housing case, and to enhance the electric insulation, and to prevent current leakage from the electrodes and the housing case, and to prevent the outlines of the electrodes and the housing case from making a short circuit.

Comparison Example

A description will be given of an electrically heated (EHC) device according to a comparison example with reference to FIG. 16, FIG. 17 and FIG. 18.

FIG. 16 is a view showing an entire structure of the EHC device 9 as the comparison example. FIG. 17 is a view showing the EHC device 9 as the comparison example having electrodes 93, 94 and the electrode terminals 930, 940 formed on an outer circumferential surface so that the electrode 93 faces the electrode 94 opposite to each other in a radial direction of the honeycomb structural body 91 when viewed from the one end surface which is perpendicular to an axial direction of the EHC device 9. FIG. 18 is a view showing the EHC device 9 as the comparison example when viewed from the other end surface which is perpendicular to an axial direction of the EHC device 9.

Similar to the EHC device 1 according to the first exemplary embodiment, the EHC device 9 as the comparison example shown in FIG. 16, FIG. 17 and FIG. 18 has a honeycomb structural body 90, the electrodes 93 and 94 in a pair, and the electrode terminals 930 and 940 in a pair. The honeycomb structural body 90 has a cell formation part 91 and the outer skin part 92 having a cylindrical shape. The electrodes 93 and 94 are formed and arranged on the outer circumferential surface 921 of the outer skin part 92 of the honeycomb structural body 90 so that the electrode 93 faces the electrode 94 relative in opposite to each other in a cross section. The pair of the electrode terminals 930 and 940 projects toward the outside of the radial direction Y of the honeycomb structural body 90 on the pair of the electrode 93 and 94.

In the structure of the EHC device 9 according to the comparison example shown in FIG. 16, FIG. 17 and FIG. 18, the electrodes 93 and 94 have the same width measured along the circumferential direction C of the outer circumferential surface 92 of the honeycomb structural body 90. Further, each of the electrodes 93 and 94 is formed parallel along the axial direction on the outer circumferential surface 92 of the honeycomb structural body 90. That is, the length edge lines of the electrode 93 are formed parallel to the length edge lines of the electrodes 94 on the outer circumferential surface 92 of the honeycomb structural body 90. Still further, the electrode terminals 930 and 940 are formed at the center parts of the electrodes 93 and 94 in the circumferential direction C of the outer circumferential surface 92 and in the axial direction X of the honeycomb structural body 90. Accordingly, as shown in FIG. 17 and FIG. 18, the pair of the electrode terminals 930 and 940 makes an angle of 180° at the axial center of the conventional EHC device and is formed along a horizontal line, which passes through the center point of the honeycomb structural body 9 when viewed from a cross section which is perpendicular to the axial direction X of the honeycomb structural body 90.

On the other hand, the EHC device 9 having the honeycomb structural body 90 according to the comparison example has a large radial size in the direction Y because of including the electrode terminals 930 and 940. That is, the EHC device 9 has a large size and needs to have a large installation area in a motor vehicle when the EHC device 9 is mounted to the motor vehicle. In order words, it is difficult to install the EHC device 9 having a large radial size according to the comparison example into a limited installation space on the floor of the motor vehicle.

As shown in FIG. 17, when at least one electrode terminal 940 of the EHC device 9 is installed so that the position of the electrode terminal 940 is below the horizontal level of the floor of the motor vehicle and is more close to the road surface, water is easily attached to the electrode terminal 940. As a result, when water is attached to the electrode terminal 940, a short circuit is often made between the electrode terminal 940 and the housing case (not shown) in which the EHC device 9 is accommodated. Further, as shown in FIG. 18, although it is possible to install the EHC device 9 to an exhaust gas pipe mounted to a motor vehicle so that the pair of the electrode terminals 930 and 940 is installed parallel to the road surface on which the motor vehicle now runs. However, such an installation structure of the comparison example requires having a large horizontal installation space in the motor vehicle.

(Features and Effects of the Electrically Heated Catalyst Device According to the Present Invention)

The EHC device according to the exemplary embodiment of the present invention has the improved electrode structure in which the electrodes face relative to each other at an angle of less than 180°. This electrode structure makes it possible to reduce the dimension of the honeycomb structural body in a radial direction of the EHC device. This makes it possible to install the EHC device to an installation space formed on an exhaust gas pipe mounted to the floor of a motor vehicle. Further, the improved and novel electrode structure makes it possible to install the EHC device to the exhaust gas pipe so that the pair of the electrode terminals of the EHC device is arranged at an upper part when compared with a horizontal direction of the EHC device. This makes it possible to escape the electrode terminals of the EHC device form being splashed with condensed water and mud when the motor vehicle runs on a road. Accordingly, this electrode structure of the EHC device can certainly avoid the electrode terminals from making a short circuit.

In the EHC device according to the exemplary embodiment, the pair of the electrodes has a constant gap on the honeycomb structural body. Further, the length edge lines of each of the electrodes, which extend along the axial direction X of the honeycomb structural body, are inclined to the virtual reference line at a predetermined angle. The virtual reference line is a virtual straight line defined on the outer skin part of the honeycomb structural body and extends parallel to an axial direction of the honeycomb structural body. As previously described, when each of the electrode terminals in the pair is formed on a center part of the corresponding electrode in the circumferential direction of the honeycomb structural body so that the electrode terminals are arranged at a constant interval along an axial direction X of the honeycomb structural body, this makes it possible to form the pair of the electrode terminals having a relative angle of less than 180°. For example, on a cross section shown in FIG. 2, the relative angle between the electrode terminals 310 and 320 is α1 (=80°) which is less than 180°. The relative angle is an angle between the electrodes formed on the outer skin part of the honeycomb structural body.

In the EHC device according to the exemplary embodiment of the present invention, the cell formation part is covered with the outer skin part of a cylindrical shape in the honeycomb structural body. The honeycomb structural body has a cross section of a circular shape when cut in a direction which is perpendicular to an axial direction of the honeycomb structural body. Because the pair of the electrodes is formed along the outer circumferential surface of the outer skin part of the honeycomb structural body, a gap or interval between the electrodes in a facing direction relative to each other varies with circumferential position. Specifically, the more the position on the electrode is separated from the center part of the electrode toward the outside (namely toward the edge part of the electrode) on the outer circumferential surface of the outer skin part along the circumferential direction, the more the gap between the electrodes measured in a radial direction (or in the facing direction) shortens. It is therefore possible for a current to more easily flow between the electrodes when the position on the electrodes is more separated from the center part of the electrodes along the circumferential direction. That is, electric power supplied through the electrode terminals is more concentrated at the length edge lines of the electrodes because a gap or interval between the length edge lines of the electrodes has the minimum distance.

In the structure of the EHC according to the first exemplary embodiment, the electrodes, that is, the length edge lines of each of the electrodes are not parallel to the virtual reference line (which are obliquely formed in an axial direction of the honeycomb structural body), but intersect with the virtual reference line. In more detail, the length edge lines are not formed parallel to the axial direction of the honeycomb structural body Accordingly, if electric power is concentrated at the length edge lines of the electrodes, the structure of the honeycomb structural body can prevent thermal stress from being concentrated at any specific axial position of the honeycomb structural body because the length edge lines are not parallel to an axial direction of the honeycomb structural body. That is, the structure of the honeycomb structural body in the EHC device according to the exemplary embodiment can diffuse thermal stress into a plurality of cells and relax the thermal stress generated in the honeycomb structural body. This makes it possible to prevent the honeycomb structural body from being damaged and broken by various stresses such as thermal stress and mechanical stress.

Further, because the electrode terminals in the pair are formed at the center part of the electrodes in the pair, respectively, in a circumference direction of the honeycomb structural body, it is possible to uniformly heat the entire of the honeycomb structural body when electric power is supplied to the electrode terminals.

Still further, in the structure of the EHC according to the first exemplary embodiment, a gap or interval between the electrodes in the pair is constant along the circumferential direction of the honeycomb structural body. That is, a gap or interval between the length edge lines of the electrodes measured in a circumferential direction is constant, and the electrodes of the pair are uniformly formed facing relative to each other with a constant interval therebetween. The electrodes are not slanting with respect to each other, namely, are parallel to each other on the outer circumferential surface of the outer skin part of the honeycomb structural body. This makes it possible to increase the area between the electrodes of the pair on the outer circumferential surface of the outer skin part of the honeycomb structural body. This structure makes it possible to uniformly heat the entire of the honeycomb structural body. Furthermore, this structure of the honeycomb structural body makes it possible to form the same gap between the length edge lines of the electrodes in the pair without shortening the gap. Accordingly, when electric power is supplied to the electrode terminals in the pair, it is possible to uniformly heat the entire of the honeycomb structural body. This prevents the honeycomb structural body from being damaged and broken by thermal stresses.

While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention which is to be given the full breadth of the following claims and all equivalents thereof. 

What is claimed is:
 1. An electrically heated catalyst device comprising: a honeycomb structural body comprising an outer skin part having a cylindrical shape and a cell formation part, the cell formation part being covered with the outer skin part; a pair of electrodes formed on an outer circumferential surface of the outer skin park, one electrode in the pair of the electrodes facing the other electrode in a radial direction of the honeycomb structural body; and a pair of electrode terminals formed on the pair of the electrodes toward outside in a radial direction of the honeycomb structural body, wherein length edge lines of one electrode and length edge lines of the other electrode extend on the outer circumferential surface of the outer skin part from one end surface to the other end surface of the honeycomb structural body in an axial direction of the honeycomb structural body so that the length edge lines of the electrodes are inclined to a virtual reference line at a predetermined angle, the length edge lines being a longitudinal part in an outline of each electrode, the virtual reference line being a virtual line defined on the outer circumferential surface of the outer skin part, which is parallel to the axial direction of the honeycomb structural body, an interval between the electrodes in the pair formed on the outer circumferential surface of the outer skin part of the honeycomb structural body measured along the circumferential direction of the honeycomb structural body is constant, the electrode terminals in the pair are formed at a circumferential center of the electrodes so that the electrode terminals keep at a predetermined interval measured in the axial direction of the honeycomb structural body, and the electrode terminals in the pair make an angle of less than 180 degrees (180°) at a radial center of the honeycomb structural body when measured on the outer circumferential surface of the outer skin part and viewed down one end surface which is perpendicular to the axial direction of the honeycomb structural body.
 2. The electrically heated catalyst device according to claim 1, wherein an insulation layer made of electrical insulation material is formed on the outer skin part of the honeycomb structural body other than in area on which the electrodes are formed.
 3. The electrically heated catalyst device according to claim 1, wherein the electrode terminals in the pair make an angle of not more than 150° when viewed from one end surface of the honeycomb structural body, and the end surface is perpendicular to an axial direction of the honeycomb structural body.
 4. The electrically heated catalyst device according to claim 1, wherein each of the length edge lines of each of the electrodes is inclined to the virtual reference line at an angle of not more than 45 degrees (45°).
 5. The electrically heated catalyst device according to claim 1, wherein the honeycomb structural body has a relationship of: D+E×sin θ1≧R/2, where D is a width of each of the electrodes measured along a circumferential direction of the outer skin part, E is a longitudinal length of each of the length edge lines of each of the electrodes, θ1 is an angle of the length edge line of each of the electrodes to the virtual reference line, and R is a circumference of an outer circumference of the honeycomb structural body in the circumferential direction C.
 6. The electrically heated catalyst device according to claim 1, wherein a distance on the outer skin part between the electrodes in the pair measured along the axial direction of the honeycomb structural body is larger than a distance on the outer skin part between the electrodes along the circumferential direction of the honeycomb structural body.
 7. The electrically heated catalyst device according to claim 1, wherein the honeycomb structural body is made of porous ceramics including SiC.
 8. The electrically heated catalyst device according to claim 3, wherein the electrode terminals in the pair make an angle of 80 degrees (80°) when viewed from one end surface of the honeycomb structural body, the end surface is perpendicular to an axial direction of the honeycomb structural body.
 9. The electrically heated catalyst device according to claim 4, wherein each of the length edge lines of each of the electrodes is inclined to the virtual reference line at an angle of 42 degrees (42°). 